Magnetic memory element and storage device using the same

ABSTRACT

A magnetic miniaturized memory element with improved thermal stability of magnetization includes a first magnetic layer, an insulating layer that is formed on the first magnetic layer, a second magnetic layer that is formed on the insulating layer, and an expanded interlayer insulating film that comes into contact with side surfaces of the first and second magnetic layers, where at least one of the first magnetic layer and the second magnetic layer is strained and deformed so as to be elongated in an easy magnetization axis direction of the first magnetic layer or the second magnetic layer or compressive strain remains in any direction in the plane of at least one of the first magnetic layer and the second magnetic layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/061,946, filed Jun. 3, 2011, being the national stage ofinternational patent application PCT/JP2009/062421, filed Jul. 8, 2009,claiming priority from Japanese patent application 2008-226446, filedSep. 3, 2008, both of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a magnetic memory element using amagnetoresistive effect and a storage device using the magnetic memoryelement, and more particularly, to a magnetic memory element and astorage device using stress or strain generated in a formed magneticlayer.

BACKGROUND ART

In recent years, a non-volatile storage device (MRAM: MagnetoresistiveRandom Access Memory) using a magnetic memory element has beendeveloped. For example, a magnetic memory element shown in FIG. 1 isgiven as an example of the related art. FIG. 1 is an enlargedcross-sectional view illustrating a portion including a magnetic memoryelement 100 in a storage device 10 including the magnetic memory element100. The magnetic memory element 100 includes a magnetic tunnel junction(MTJ) portion 13, and the MTJ portion 13 is sandwiched between a lowerelectrode 14 and an upper electrode 12. The MTJ portion 13 has amulti-layered structure of a fixed layer 22, an insulating layer 21, anda recording layer 20 formed on the lower electrode 14 in this order. Thefixed layer 22 and the recording layer 20 are made of a ferromagneticmaterial. The lower electrode 14 is connected to a drain region 24provided in a substrate 15, and a source region 25 is also provided inthe substrate 15 at a predetermined distance from the drain region 24. Agate line 16 is formed above the drain region 24 and the source region25 so as to be insulated therefrom. In this way, a MOSFET (metal oxidesemiconductor field effect transistor) having the terminals of the drainregion 24, the source region 25, and the gate line 16 is formed. Inaddition, a contact portion 17 and a word line 18 are formed in thisorder on the source region 25. The upper electrode 12 is connected to abit line 11. The word line 18 and the bit line 11 are insulated fromeach other by an interlayer insulating film 23 and are connected to acontrol circuit (not shown). The storage device 10 selects the magneticmemory element 100, reads information stored in the magnetic memoryelement 100, and writes information to the magnetic memory element 100.

Next, the principle of a data read operation of the magnetic memoryelement 100 will be described. First, the insulating layer 21 isprovided between the recording layer 20 and the fixed layer 22, and theinsulating layer 21 has a small thickness of 3 nm or less. Therefore,when an external voltage is applied, a small amount of current (tunnelcurrent) flows from the recording layer 20 to the fixed layer 22 throughthe insulating layer 21. Since the recording layer 20 and the fixedlayer 22 are ferromagnetic bodies, they have spontaneous magnetization(hereinafter, simply referred to as “magnetization”), and the tunnelcurrent is increased or decreased by a combination (magnetizationarrangement) of the magnetization directions of the recording layer 20and the fixed layer 22. That is, when the direction of the magnetization102A of the recording layer 20 is identical to (parallel to) thedirection of the magnetization 102B of the fixed layer 22, the tunnelcurrent passing through the insulating layer 21 increases. On the otherhand, when the direction of the magnetization 102A of the recordinglayer 20 is opposite to (anti-parallel to) the direction of themagnetization 102B of the fixed layer 22, the tunnel current decreases.This property is called a tunneling magnetoresistance effect, which isdescribed in detail in Non-patent Document 1: Inomata Koichiro,“Non-volatile magnetic memory MRAM,” Kogyo Chosakai Publishing Co.,Ltd., November 2005 (hereinafter Non-patent Document 1).

This property can be used to determine whether the magnetizationdirections of the recording layer 20 and the fixed layer 22 areidentical to each other, which is defined as “0”, or the magnetizationdirections of the recording layer 20 and the fixed layer 22 are oppositeto each other, which is defined as “1”, on the basis of the magnitude ofthe tunnel current. That is, when the direction of the magnetization102B of the fixed layer 20 is fixed, it is possible to read informationstored in the recording layer 20 as the magnetization direction. Themagnetization directions of the recording layer 20 and the fixed layer22 are maintained even when energy, such as a current, is not supplied.Therefore, when the magnetic memory element 100 shown in FIG. 1 isintegrated, it is possible to achieve a non-volatile storage device(memory) that retains data even when the power source is turned off.

Next, the principle of a data write operation will be described. In therelated art, in order to write data, a method has been used in which amagnetic field is generated in the vicinity of the recording layer 20due to a current and the magnetization direction of the recording layer20 is changed by the magnetic field. However, in this method, as thesize of an element is reduced, the amount of current required for awrite magnetic field increases. As such, since the current valueincreases with a reduction in the size of the element, it is difficultto reduce the size of the magnetic memory element, that is, to increaserecording density. Therefore, in recent years, a method has been usedwhich makes a spin-polarized current flow from the fixed layer 22 to therecording layer 20 to control the magnetization direction of therecording layer 20. This method is called an STT (Spin Torque Transfer)method and is described in detail in Non-patent Document 1. In the STTmethod, a spin-polarized current for writing is reduced with a reductionin the size of the element. Therefore, it is easy to increase recordingdensity.

A gigabit-class magnetic memory device has been developed by the use ofthe perpendicular magnetization film and the STT method. The magneticmemory element shown in FIG. 1 has the same operation as the magneticmemory element disclosed in Patent Document 1: U.S. Patent ApplicationPublication No. 2007/297220.

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, when the magnetic memory element is integrated to manufacturean MRAM, there is a problem in that the thermal stability of recordedmagnetization is damaged.

In general, KuV/k_(B)T is used as a factor, which is an index of thethermal stability of the magnetization of a ferromagnetic layer (where Vis the volume of the ferromagnetic layer, k_(B) is the Boltzmannconstant, and T is the temperature). From this relationship, when theshape of the ferromagnetic layer is given, the thermal stability isdetermined by only the magnetic anisotropy energy Ku and the temperatureT. As described above, since a magnetic anisotropy energy variesdepending on the internal stress of the magnetic layer, the thermalstability of the recorded magnetization of the magnetic memory elementvaries depending on the internal stress of the recording layer 20. Inorder to integrate the magnetic memory element to be used as an MRAM, itis necessary to set the value of a thermal stability factor KuV/k_(B)Tto 60 or more. That is, in order to manufacture an MRAM, it is necessaryto increase the thermal stability of the magnetization of the magneticlayer in each element. In order to increase the thermal stability, themagnetic anisotropy energy Ku needs to increase.

When the magnetic memory element is integrated to manufacture an MRAM, asemiconductor integrated circuit manufacturing process is used. However,in this case, a stress of about 100 MPa remains in the element. Theinventors consider that the thermal stability is reduced due to aresidual stress. That is, when an internal stress σ is generated in themagnetic layer by the semiconductor manufacturing process,magnetoelastic energy is changed according to the relationshipH_(el)=−(3/2)λσ (where λ is a magnetostriction constant determined by amagnetic body and the typical value of the magnetostriction constant isin the range of about 100 ppm to 1000 ppm in a rare earth-transitionmetal alloy). The magnetoelastic energy is a portion of the magneticanisotropy energy Ku. Therefore, when the internal stress σ is generatedby the semiconductor manufacturing process, the magnetic anisotropyenergy Ku of a magnetic body of the magnetic memory element is changed.As a result, the thermal stability factor is affected by the change inthe magnetic anisotropy energy Ku.

Next, the influence of residual stress when the magnetic memory elementis integrated to manufacture an MRAM is estimated in detail. Forexample, in a CMOS process, the amount of stress that is generated andremains in each element in the semiconductor manufacturing process formanufacturing an MRAM is about several hundreds of MPa. In a device thatdoes not use magnetism, a residual stress of several hundreds of MPacauses little problem. In contrast, in the MRAM, if a case in which themagnetostriction constant is 1000 ppm and stress is 100 MPa isconsidered, magnetoelastic energy by the influence of stress is about10⁵ J/m³ (=10⁶ erg/cm³). For example, in a CoCrPt-based alloy used forperpendicular magnetic recording, magneto-crystalline anisotropy energyis about 10⁵ J/m³ to 10⁶ J/m³ (=10⁶ erg/cm³ to 10⁷ erg/cm³). That is,magnetoelastic energy is the same order of magnitude asmagneto-crystalline anisotropy energy. As such, the influence of theinternal stress of the MRAM is closely related to the stability ofmagnetization. Since a residual stress has a great effect on the totalsum of magnetic anisotropy energy, it is necessary to appropriatelyconsider the residual stress generated by the semiconductormanufacturing process during the manufacture of the MRAM.

In particular, as shown in FIG. 2, the magnetic layer is strained anddeformed due to a residual stress (for example, stress 101). As aresult, when magnetic anisotropy energy is low, the magnetization in theperpendicular direction is likely to be inclined in the in-planedirection due to a thermal fluctuation. FIG. 2 is a plan view and across-sectional view illustrating a magnetic layer 20 with a circularshape and shows a case in which the residual stress is a tensile stress.As such, when the residual stress acts such that the magnetizationdirection is inclined from the perpendicular direction to the in-planedirection, there is a concern that the thermal stability ofmagnetization will be damaged and it will be difficult to obtain athermal stability required for an MRAM.

The inventors found out the above-mentioned problems and found that itwas possible to prevent the thermal stability of the magnetization ofthe magnetic memory element from being damaged by appropriatelycontrolling stress or strain generated in the ferromagnetic layer of themagnetic memory element in the semiconductor manufacturing process andthe stress or strain could be used to improve the thermal stability ofthe magnetization, thereby achieving the invention.

Means for Solving the Problems

According to an aspect of the invention, a magnetic memory elementincludes a first magnetic layer, an insulating layer that is formed onthe first magnetic layer, and a second magnetic layer that is formed onthe insulating layer. At least one of the first magnetic layer and thesecond magnetic layer is strained and deformed so as to be elongated inan easy magnetization axis direction of the magnetic layer. According tothis structure, in the first magnetic layer and the second magneticlayer, magnetic anisotropy energy Ku increases, and it is possible toimprove the thermal stability of the magnetization of a recording layer.

In the above-mentioned aspect of the invention, the magnetic memoryelement may further include an underlayer or a substrate that isprovided below the first magnetic layer and is made of a material with athermal expansion coefficient greater than that of the first magneticlayer. The underlayer or the substrate may be contracted to compress thefirst magnetic layer, thereby generating the compressive stress. Sincethe first magnetic layer is compressed by the contraction of theunderlayer or the substrate, the compressive stress is generated in thefirst magnetic layer. A compressive stress is also generated in thesecond magnetic layer. Therefore, the compressive stress can be used toimprove the thermal stability of the magnetization of the first magneticlayer and the second magnetic layer. The effect of improving thermalstability is noticeable in the first magnetic layer.

The invention may be implemented as a storage device.

Effects of the Invention

According to the invention, it is possible to generate residual stressor strain deformation in a magnetic layer in a semiconductormanufacturing process and actively use the generated stress or strain toimprove the thermal stability of the magnetization of the magneticlayer, thereby preventing the magnetization direction of the magneticlayer from being inclined or improving the thermal stability of recordedmagnetization.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating an example of thestructure of a magnetic memory element according to the related art.

FIG. 2 is a conceptual diagram illustrating an aspect in which thestability of magnetization is reduced due to stress and magnetization isinclined.

FIG. 3 is a diagram illustrating a state in which compressive stress isapplied to the center of a magnetic layer in the in-plane direction.

FIG. 4 is a diagram illustrating a state in which stress is applied tothe magnetic layer in a one-axis direction of the in-plane direction.

FIG. 5 is a cross-sectional view illustrating the structure of amagnetic memory element (Example 1) according to a first embodiment ofthe invention.

FIG. 6 is a cross-sectional view illustrating the structure of amagnetic memory element (Example 2) according to a second embodiment ofthe invention.

FIG. 7 is a cross-sectional view illustrating the structure of amagnetic memory element (Example 3) according to a third embodiment ofthe invention.

FIG. 8 is a cross-sectional view illustrating the structure of an MRAM(Example 4) according to a fourth embodiment of the invention.

FIG. 9 is a cross-sectional view illustrating the structure of themagnetic memory element according to the third embodiment and Example 3of the invention.

FIG. 10 is a diagram illustrating a method of manufacturing the magneticmemory element according to Example 3 of the invention.

FIG. 11 is a characteristic diagram illustrating a method of measuringmagnetic anisotropy energy.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, exemplary embodiments of the invention will be describedwith reference to the accompanying drawings.

In an aspect of the invention, a strain deformation is actively used toprevent the deterioration of the thermal stability of the magnetizationof a recording layer or improve the thermal stability. Next, theoperation of the strain deformation in the above-mentioned case will bedescribed. It is assumed that there is a magnetic layer without a straindeformation as represented by a two-dot chain line in a plan view and afront view of FIG. 3 and the stress in a radius direction is uniformlyapplied to the center of the magnetic layer from all directions, thatis, a centrosymmetric stress is applied. As a result, as represented bya solid line in FIG. 3, the magnetic layer is strained and deformed suchthat the size (radius or diameter) thereof in the plane is slightlyreduced and the thickness thereof slightly increases. An arrow in theplan view of FIG. 3 indicates the displacement of a circumferentialportion in the deformation. In the invention, this state is defined as astate in which a centrosymmetric compressive stress is applied in thein-plane direction. As such, when a compressive stress is applied in thein-plane (film surface) direction, the magnetic layer is compressed inthe in-plane direction such that the size thereof is reduced and iselongated in the longitudinal direction (perpendicular direction).Therefore, when a compressive stress is applied to the in-planedirection, a perpendicular magnetization film is strained and deformedso as to be elongated in the easy magnetic axis direction, that is, thefilm thickness direction. In this way, it is possible to increase themagnetic anisotropy energy of the magnetization film and thus improvethe thermal stability of perpendicular magnetization in a directionperpendicular to the film. For ease of understanding, a smalldeformation is enlarged in the drawings.

FIG. 4 shows another aspect of the strain deformation. FIG. 4 is a planview and a front view showing a magnetic layer. In FIG. 4, a compressivestress is applied from both sides (the vertical direction of the planview) in one direction in the plane and the stress is applied so as tobe symmetric with respect to the axis, not the center, unlike FIG. 3. Inthe invention, this state is defined as a state in which a compressivestress is applied in a one-axis direction of the in-plane direction.When a compressive stress is applied in a one-axis direction of thein-plane direction, the magnetic layer is strained and deformed so as tobe contracted in the vertical direction and be elongated in thehorizontal direction of the plan view. In addition, the magnetic layeris strained and deformed so as to be elongated in the longitudinaldirection (perpendicular direction) of the front view. Therefore, inthis case, when the first magnetic layer is an in-plane magnetizationfilm and an elongated direction (the horizontal direction of the planview) is aligned with the easy magnetization axis, magnetic anisotropyenergy increases. Even when the first magnetic layer is a perpendicularmagnetization film, magnetic anisotropy energy increases since the firstmagnetic layer is elongated in the perpendicular direction. Therefore,when a compressive stress is applied in the one-axis direction of thein-plane direction, it is possible to strain and deform the magneticlayer so as to be elongated in the easy magnetization axis direction,regardless of whether the magnetization layer is a horizontalmagnetization film or a perpendicular magnetization film. As a result,it is possible to improve the thermal stability of the magnetization ofthe magnetization layer.

According to a preferred aspect of the invention, the first magneticlayer and the second magnetic layer may be perpendicular magnetizationfilms, and at least one of the first magnetic layer and the secondmagnetic layer may be strained and deformed so as to be elongated in adirection perpendicular to the surface of the film. According to thisstructure, the stress generated in the first magnetic layer and thesecond magnetic layer can be used to improve the stability of recordedmagnetization in the perpendicular magnetization film.

According to another preferred aspect of the invention, the firstmagnetic layer and the second magnetic layer may be in-planemagnetization films, and at least one of the first magnetic layer andthe second magnetic layer may be strained and deformed such that themagnetic layer has an elliptical or rectangular in-plane shape and iselongated in a long axis direction. According to this structure, it ispossible to increase magnetic anisotropy energy and improve the thermalstability of recorded magnetization in the in-plane magnetization film.

In the invention, the magnetic memory element may further include aninterlayer insulating film that comes into contact with a side surfaceof the first magnetic layer and a side surface of the second magneticlayer and insulates the side surface of the first magnetic layer and theside surface of the second magnetic layer from other metal materials. Atleast one of the first magnetic layer and the second magnetic layer maybe compressed by the interlayer insulating film from the side surface tobe strained and deformed. The interlayer insulating film compresses thefirst magnetic layer and the second magnetic layer from the side surfaceto generate a compressive stress in the in-plane direction of the firstand second magnetic layers. In this way, it is possible to improve thethermal stability of recorded magnetization.

In the invention, the magnetic memory element may further include anunderlayer or a substrate that is provided below the first magneticlayer and is made of a material with a thermal expansion coefficientgreater than that of the first magnetic layer. The underlayer or thesubstrate may be contracted to compress the first magnetic layer,thereby straining and deforming at least one of the first magnetic layerand the second magnetic layer. That is, since the first magnetic layeris compressed by the contraction of the underlayer or the substrate, acompressive stress is generated in the first magnetic layer. Thecompressive stress is also generated in the second magnetic layer.Therefore, the compressive stress can be used to improve the thermalstability of the magnetization of the first magnetic layer and thesecond magnetic layer. The effect of improving thermal stability isnoticeable in the first magnetic layer.

According to an aspect of the invention, a magnetic memory elementincludes a first magnetic layer, an insulating layer that is formed onthe first magnetic layer, and a second magnetic layer that is formed onthe insulating layer. A compressive stress remains in any direction inthe plane of at least one of the first magnetic layer and the secondmagnetic layer. In the first magnetic layer and the second magneticlayer, magnetic anisotropy energy Ku increases, and it is possible toimprove the thermal stability of recorded magnetization. The compressivestress applied in any direction in the plane includes a compressivestress applied to the center of the plane or uniaxial compressivestress.

In the invention, the magnetic memory element may further include aninterlayer insulating film that comes into contact with a side surfaceof the first magnetic layer and a side surface of the second magneticlayer and insulates the side surface of the first magnetic layer and theside surface of the second magnetic layer from other metal materials.The interlayer insulating film compresses the first magnetic layer orthe second magnetic layer from the side surface to generate thecompressive stress. According to this structure, the interlayerinsulating film compresses the first magnetic layer and the secondmagnetic layer from the side surface to generate a compressive stress inthe first and second magnetic layers. In this way, it is possible toimprove the thermal stability of recorded magnetization.

In any aspect of the invention, the first magnetic layer or the secondmagnetic layer may be a single-layer film made of a rareearth-transition metal alloy or a multi-layered film of a rareearth-transition metal alloy and a spin-polarized film. According tothis structure, since the thermal stability of the magnetization of therare earth-transition metal alloy is greatly changed by stress, it ispossible to effectively use the stress generated in the first magneticlayer and the second magnetic layer to improve the stability of recordedmagnetization. The rare earth-transition metal alloy includes ascomponents a rare earth-based element, such as Gd, Tb, or Dy, and atransition metal element, such as Fe or Co. In addition, thespin-polarized film means a magnetic film in which spin is completelypolarized in the Δ1 band, such as a Fe, FeCo, or FeCoB film. It ispossible to increase an effective spin polarization ratio by combiningthe spin-polarized film with an insulating layer having fourfoldsymmetry in the stacking direction, such as an MgO film, to form a spintunnel junction. In this structure, it has been experimentally andtheoretically found that it is possible to optimize conditions to obtaina magnetoresistance ratio of about 1000%.

In this case, the first magnetic layer or the second magnetic layer maybe a multi-layered film of a rare earth-transition metal alloy and aFeCo alloy thin film or a FeCoB alloy thin film. It has beenexperimentally found that, when the FeCo alloy thin film has amulti-layered structure of FeCo, MgO, and FeCo, a magnetoresistanceratio of 200% or more is obtained, and the FeCo alloy thin film can havegood characteristics as the spin-polarized film. In addition, since theFeCoB alloy thin film is an amorphous thin film, it is possible to forma large film with uniform film quality, without depending on a base.

In any aspect of the invention, the first magnetic layer or the secondmagnetic layer may be a single-layer granular perpendicularmagnetization film or a multi-layered film of a granular perpendicularmagnetization film and a spin-polarized film. It is possible tostabilize the magnetization direction of the granular perpendicularmagnetization film to the perpendicular direction using stress andimprove the thermal stability of recorded magnetization. The granularperpendicular magnetization film means a magnetic film in which granularor columnar chunks of perpendicular magnetization metal are dispersed inan insulator or a non-magnetic material, such as CoCrPt—SiO₂. In thiscase, the first magnetic layer or the second magnetic layer may be amulti-layered film of a granular perpendicular magnetization film and aFeCo alloy thin film or a FeCoB alloy thin film.

The magnetic memory element according to an embodiment of the inventionmay be applied to a storage device that uses the magnetic memory elementas a storage element. In this case, the storage device may include aplurality of the magnetic memory elements and a sealing package that isobtained by curing a liquid sealing material and has the plurality ofmagnetic memory elements sealed therein. By contraction when the sealingmaterial is cured, the first magnetic layer or the second magnetic layerof the magnetic memory element may be strained and deformed so as to beelongated in a direction perpendicular to the surface of the layer or acompressive stress may remain in any direction in the plane of at leastone of the first magnetic layer and the second magnetic layer. That is,a tensile force acting on the element when the sealing agent is cured isused to elongate the magnetic layer (first or second magnetic layer) inthe perpendicular direction of the storage element. When the magneticlayer is elongated in the perpendicular direction, it is contracted inthe in-plane (the surface of the layer) direction. Therefore, acompressive stress is generated in the in-plane direction. Thecompressive stress can be used to improve the thermal stability ofrecorded magnetization.

The storage device according to the invention may include a die frame onwhich a substrate having a plurality of the magnetic memory elementsprovided thereon is placed and a sealing package that is obtained bycuring a liquid sealing material and has the plurality of magneticmemory elements and the die frame sealed therein. The die frame may bewarped to strain and deform the first magnetic layer or the secondmagnetic layer of the magnetic memory element so as to be elongated in adirection perpendicular to the surface of the layer or make acompressive stress remain in any direction in the plane of the firstmagnetic layer or the second magnetic layer. The sealing material may becured with the die frame being warped, thereby sealing the die frame inthe sealing package.

[First Embodiment]

Hereinafter, exemplary embodiments of the invention will be describedwith reference to the drawings. FIG. 5 shows a first embodiment of theinvention. In FIG. 5, the same components as those in FIG. 1 are denotedby the same reference numerals and a description thereof will beomitted. In FIG. 5, an interlayer insulating film 23X is used to applycompressive stress to a fixed layer 22 and a recording layer 20 from theside surfaces of the fixed layer 22 and the recording layer 20, therebystraining and deforming the fixed layer 22 and the recording layer 20such that an in-plane shape extending in the easy magnetization axisdirection is obtained. In this way, the thermal stability of recordedmagnetization is improved by a compressive stress or strain deformationextending in the easy magnetization axis direction.

The internal stress of the interlayer insulating film 23 depends on theconditions (for example, gas pressure, a target composition, and asputtering voltage) of a process of forming the interlayer insulatingfilm 23. In the related art, when the internal stress of the interlayerinsulating film 23 increases, the interlayer insulating film is strainedand deformed, and the strain deformation causes the distortion of, forexample, an MTJ portion 13, an upper electrode 12, or a lower electrode14 coming into contact with the interlayer insulating film 23. For thisreason, it is not preferable to increase the internal stress of theinterlayer insulating film 23. That is, in the related art, theinterlayer insulating film 23 is formed by adjusting the conditions of afilm forming process such that an internal stress is as small aspossible. For example, the interlayer insulating film 23 is formed bygenerating plasma using both a high-frequency power source and alow-frequency power source and adjusting the ratio of high frequencypower and low frequency power such that the stress generated in theinterlayer insulating film 23 is minimized

In contrast, in the structure according to the embodiment of theinvention shown in FIG. 5, the strain deformation of the interlayerinsulating film 23 is actively used. That is, in a process of formingthe interlayer insulating film 23, the interlayer insulating film 23 isformed such that the internal stress thereof increases, therebygenerating expansion (strain deformation). The interlayer insulatingfilm formed under the above-mentioned conditions is shown as theinterlayer insulating film 23X. In the embodiment shown in FIG. 5, therecording layer 20 and the fixed layer 22 are compressed in the in-planedirection by the expanded interlayer insulating film 23X. Therefore, acompressive stress is generated in the recording layer 20 and the fixedlayer 22, and the compressive stress changes the internal magneticanisotropy energy of the recording layer 20 and the fixed layer 22 suchthat the thermal stability of magnetization is improved. In this way, itis possible to improve the thermal stability of recorded magnetization.

When the recording layer 20 and the fixed layer 22 are not perpendicularmagnetization films, it is necessary to form the MTJ portion 13 in, forexample, an elliptical shape or a rectangular shape in the plane. Incontrast, when the layers are perpendicular magnetization films, it ispossible to set the aspect ratio of the element shape to 1. The reasonis as follows. When the magnetization direction is in-planemagnetization, the symmetry of the in-plane shape of the element isreduced and it is necessary to limit the magnetization direction.However, when the magnetization direction can be aligned with adirection perpendicular to the surface of the film, it is not necessaryto limit the magnetization direction. Therefore, in the magnetic memoryelement shown in FIG. 5, when the recording layer 20 and the fixed layer22 are perpendicular magnetization films as shown in FIG. 1, it ispossible to form an element in a high-symmetry shape, such as a squareshape or a circular shape, in the plane and thus reduce the area of theelement, as compared to the structure in which an in-plane magnetizationfilm is used. As a result, it is possible to increase the density ofelements.

[Second Embodiment]

FIG. 6 shows a second embodiment. The structure shown in FIG. 6 differsfrom the structure shown in FIG. 1 in that the lower electrode 14 ismade of a material with a thermal expansion coefficient greater thanthose of the recording layer 20 and the fixed layer 22. That is, in thisembodiment, the contractile force of the lower electrode 14 is used tocompress the fixed layer 22 and the recording layer 20.

First, when the fixed layer 22 and the recording layer 20 are formed,the lower electrode 14 is heated to be expanded. When the lowerelectrode 14 is cooled to a room temperature after the fixed layer 22and the recording layer 20 are formed, the fixed layer 22 and therecording layer 20 are contracted by the contractile force of the lowerelectrode 14. A stress 101 is generated in the fixed layer 22 and therecording layer 20 by the contraction. Since the stress 101 is acompressive stress, the thermal stability of recorded magnetization canbe improved by the same effect as that of the structure shown in FIG. 5.

[Third Embodiment]

FIG. 7 shows a third embodiment. In the structure shown in FIG. 7, thecontraction of a sealing agent (epoxy resin) used to seal an integratedmagnetic memory element in a package is used to generate a compressivestress in the in-plane direction of the recording layer 20 and the fixedlayer 22.

In general, when an element subjected to a semiconductor manufacturingprocess is packed, the element is sealed by a sealing material, such asan epoxy resin, in order to protect the inner element from the influenceof an environment. In this embodiment, when the element is sealed by theepoxy resin, a resin that is cured to be contracted is used. In thisway, as shown in FIG. 7, the element is drawn in a directionperpendicular to the surface of the film. When the element is drawn inthe perpendicular direction, a magnetic layer is contracted in thein-plane direction and a compressive stress is generated in the in-planedirection. It is possible to improve the thermal stability of therecorded magnetization of a perpendicular magnetization film by the sameeffect as that in FIG. 5, which is obtained by the compressive stress.

[Fourth Embodiment]

FIG. 8 shows a fourth embodiment. In FIG. 8, a magnetic memory elementis integrated into an MRAM, and an MRAM chip 1 is mounted on a die frame41. The MRAM chip 1 is connected to a lead frame 43 by bonding wires 42.The MRAM chip 1 and the die frame 41 are sealed in a resin package 44.In this embodiment, when the MRAM chip is sealed in the resin package inthe last stage of the semiconductor manufacturing process, the resin iscured with the die frame 41 and the MRAM chip 1 being warped. In thisway, a compressive stress is applied to the magnetic layer of the MRAMchip. Although not shown in the drawings, holding frames surrounding thedie frame 41 and the MRAM chip 1 are provided in order to maintain thewarped state of the die frame 41 and a substrate of the MRAM chip, andthe holding frames come into contact with the lower sides of the leftand right ends of the die frame 41 in FIG. 8 and the upper side of theMRAM chip 1 in the downward and upward directions to generate a stressin the MRAM chip 1. In this way, it is possible to seal each holdingframe in the resin package. In this embodiment, the resin that is curedto be contacted may not be necessarily used.

Example 1

A method of manufacturing a magnetic memory element according to Example1 which is manufactured by the first embodiment will be described belowreferring to FIG. 5 again. First, a drain region 24, a source region 25,and a gate electrode 16 are formed on a Si substrate (silicon wafer) 15by a CMOS process. Then, an Al film (5 nm) is formed by a magnetronsputtering method. Then, a lower electrode 14 is formed on the drainregion 24 and a contact 17 is formed on the source region 25 byphotolithography. In addition, a Cu film (10 nm) is formed by themagnetron sputtering method, and a gate line 18 is formed on the sourceregion 25 by photolithography.

Then, TbFeCo (5 nm), FeCoB (1 nm), MgO (1 nm), FeCoB (1 nm), TbFeCo (5nm), Ta (5 nm), Ru (5 nm), and Ta (3 nm) films are formed in this order,and the multi-layered film is microfabricated into a circular elementwith a diameter of 50 nm to 100 nm by a photolithography process. Atthat time, an interlayer insulating film (SiN) is formed by a plasma CVD(chemical vapor deposition) process while a resist remains. In theplasma CVD process, a reaction gas is a mixed gas of silane (SiH₄) andammonia (NH₃), the substrate is heated at 400° C., and a 13.56-MHzhigh-frequency power source is used as a power source for generatingplasma to generate plasma with an output of about 1 kW to 2.5 kW. Afterthe interlayer insulating film is formed with a thickness of about 100nm in this way, the resist used in the previous photolithography processis cleaned with a solvent, such as acetone or NMP(N-methyl-2-pyrrolidone). Then, Ta (10 nm), Cu (500 nm), and Ta (10 nm)films are formed in this order by magnetron sputtering and a Ta/Cu/Tamulti-layered portion is processed in a bit line shape byphotolithography. In this way, it is possible to manufacture themagnetic memory element according to Example 1 of the invention.

Next, the effect of the structure of the magnetic memory elementaccording to Example 1 will be described. In the plasma CVD processduring the formation of the interlayer insulating film 23, when thefrequency of the plasma generating power source is high (for example,13.56 MHz), a tensile stress is generated in the SiN film, and when thefrequency is low (for example, 250 kHz), a compressive stress isgenerated in the SiN film. In the related art, it was considered that anincrease in the internal stress of the interlayer insulating film 23 wasnot preferable. That is, in the related art, in the plasma CVD process,for example, both the high-frequency power source and the low-frequencypower source were used to generate plasma (dual frequency), and theratio of high frequency power and low frequency power was adjusted tominimize the stress generated in the interlayer insulating film 23.

In contrast, in the structure shown in FIG. 5, the strain deformation ofthe interlayer insulating film 23 is actively used. That is, in theplasma CVD process of the interlayer insulating film 23, since the filmis formed by, for example, high frequency plasma, a tensile stress (˜600MPa) is generated in the interlayer insulating film 23. The interlayerinsulating film 23 is expanded in the forward direction in the plane ofthe film by the tensile stress and is then strained and deformed(˜0.15%). The expanded interlayer insulating film 23 presses the sideportions of the surface recording layer 20 and the fixed layer 22 in alldirections to be compressed in the in-plane direction. At that time,when it is assumed that the strain deformation of the interlayerinsulating film 23 is transferred to the recording layer 20 and thefixed layer 22, a compressive stress of about 150 MPa is generated inthe recording layer 20 and the fixed layer 22. The compressive stresschanges the internal magnetic anisotropy energy of the recording layer20 and the fixed layer 22 such that the thermal stability ofmagnetization is improved. In a thin film made of an alloy, such asTbFeCo, TbFe, GdFeCo, GdFe, DyFeCo, or DyFe which is known as a rareearth-transition metal alloy, a magnetostriction constant λ, is changedin the range of 100 ppm to 1000 ppm depending on a composition. If acomposition is adjusted such that the magnetostriction constant is 1000ppm, magnetic anisotropy energy is improved by about 1.5×10⁵ J/m³(=1.5×10⁶ erg/cm³), and thermal stability is improved by about 200KuV/k_(B)T. Therefore, it is possible to ensure sufficient thermalstability of an MRAM.

In Example 1, a single high-frequency power source (˜13.56 MHz) is usedas the power source for generating plasma during the formation of theinterlayer insulating film 23. In addition to the high-frequency powersource, a low-frequency power source (˜250 kHz) may be used in order toimprove the quality of a film, that is, the property of a film, such asstep coverage or moisture resistance. In this case, when the outputpower of the high-frequency power source is more than that of thelow-frequency power source, it is possible to improve the quality of afilm (step coverage and moisture resistance) while maintaining thethermal stability of recorded magnetization.

In Example 1, plasma CVD is used as a method of forming the interlayerinsulating film 23, but thermal CVD may be used to form the interlayerinsulating film 23. For example, when the entire magnetic memory elementis heated in a mixed gas of a silane (SiH₄) gas and an ammonia (NH₃) gasat a temperature of 900° C. or more, it is also possible to generate atensile stress in the interlayer insulating film 23. In Example 1, theSiN film is used as the interlayer insulating film 23. However, forexample, a SiO₂ film, a PSG film, and a TEOS film may be used as theinterlayer insulating film 23. In this case, it is possible to obtainthe same effect as described above.

Example 2

FIG. 6 shows the structure of a magnetic memory element according toExample 2 which is manufactured by the second embodiment of theinvention. In Example 2, a magnetic layer (a recording layer 20 and afixed layer 22) and a lower electrode 14 are made of materials withdifferent thermal expansion coefficients and a compressive stress isapplied to the fixed layer 22 and the recording layer 20. Amanufacturing method according to Example 2 will be described withreference to FIG. 6. First, similar to FIG. 5, a drain region 24, asource region 25, and a gate electrode 16 are formed on a Si substrate15 by a CMOS process. Then, an A1 film (5 nm) is formed by a magnetronsputtering method. Then, the lower electrode 14 is formed on the drainregion 24 and a contact 17 is formed on the source region 25 byphotolithography. In addition, a Cu film (10 nm) is formed by themagnetron sputtering method, and a gate line 18 is formed on the sourceregion 25 by photolithography.

Then, the entire Si substrate 15 is heated to about 300° C. to 400° C.Then, TbFeCo (5 nm), FeCoB (1 nm), MgO (1 nm), FeCoB (1 nm), TbFeCo (5nm), Ta (5 nm), Ru (5 nm), and Ta (3 nm) films are formed in this orderwhile a high temperature of 300° C. to 400° C. is maintained. Then, themulti-layered film is cooled to a room temperature. Then, themulti-layered film is microfabricated by a photolithography process suchthat the in-plane shape thereof is a circle with a diameter of 50 nm to100 nm. In addition, an interlayer insulating film (SiN) is formed by aplasma CVD process while a resist remains. In the plasma CVD process, areaction gas is a mixed gas of silane (SiH₄) and ammonia (NH₃), thesubstrate is heated at 400° C., and a 13.56-MHz high-frequency powersource and a 250-kHz low-frequency power source are used as a powersource for generating plasma to generate plasma with a total output ofabout 1 kW to 2.5 kW. After the interlayer insulating film is formedwith a thickness of about 100 nm, the resist used in the previousphotolithography process is cleaned with acetone or NMP. Then, Ta (10nm), Cu (500 nm), and Ta (10 nm) films are formed in this order bymagnetron sputtering and a Ta/Cu/Ta multi-layered portion is processedin a bit line shape by photolithography. In this way, the structureaccording to Example 2 is manufactured.

Next, the effect of the structure of the magnetic memory elementaccording to Example 2 will be described. When aTbFeCo/FeCoB/MgO/FeCoB/TbFeCo film is formed, the substrate is heatedand the lower electrode 14 is thermally expanded. In this state, themagnetic layer is formed. When the thermal expansion coefficient of Al(lower electrode 14) in the range of the room temperature to 400° C. isin the range of about 23 ppm/K to 28 ppm/K and the thermal expansioncoefficient of TbFeCo is 8 ppm/K, which is a general value of thethermal expansion coefficient of an amorphous Fe-based alloy, acompressive stress is applied to the TbFeCo layer from the interfacewith the lower electrode 14 by the difference between the thermalexpansion coefficients, and a maximum compressive stress of 650 MParemains in the layer. When the compressive stress is considered asmagnetic anisotropy energy similar to the above, magnetic anisotropyenergy is increased by 6.5×10⁵ J/m³ (=6.5×10⁶ erg/cm³). As a result,thermal stability is considerably improved.

Preferably, during the writing of data, since the element is heated by acurrent flowing through the element, a contractile stress due to thedifference between the thermal expansion coefficients is reduced, andthermal stability is reduced. That is, during writing, it is possible toreduce thermal stability to decrease the amount of current required forwriting. As described above, according to the magnetic memory element ofExample 2, it is possible to improve the retention characteristics ofthe magnetic memory element and reduce the amount of current required towrite data.

In the structure of the magnetic memory element according to Example 2,the lower electrode is made of aluminum (Al). However, the lowerelectrode may be made of other metal materials with a large thermalexpansion coefficient, such as silver (Ag), gold (Au), and copper (Cu).The thermal expansion coefficients of the metal materials are asfollows: silver: 20 ppm/K; gold: 14 ppm/K; and copper: 17 ppm/K.

Example 3

A magnetic memory element according to Example 3 which is manufacturedas the third embodiment of the invention has a structure shown in FIG.9. In FIG. 9, a magnetic layer is formed with a Si substrate 15 warpedin a mountain shape, as shown in FIG. 10, and the Si substrate 15returns to a flat state after the magnetic layer is formed. In this way,a compressive stress remains in the magnetic layer. A method ofmanufacturing the structure according to Example 3 will be described.First, similar to FIG. 5, a drain region 24, a source region 25, and agate electrode 16 are formed on the Si substrate 15 by a CMOS process.Then, an Al film (5 nm) is formed by a magnetron sputtering method.Then, a lower electrode 14 is formed on the drain region 24 and acontact 17 is formed on the source region 25 by photolithography. Inaddition, a Cu film (10 nm) is formed by the magnetron sputteringmethod, and a gate line 18 is formed on the source region 25 byphotolithography.

Then, as shown in FIG. 10, the Si substrate 15 is fixed by a jig so asto be warped in a mountain shape with a curvature radius R of 2 m. Inthis state, TbFeCo (5 nm), FeCoB (1 nm), MgO (1 nm), FeCoB (1 nm),TbFeCo (5 nm), Ta (5 nm), Ru (5 nm), and Ta (3 nm) films are formed inthis order. Then, the warped Si substrate 15 is removed from the jig tohave elasticity. Then, the multi-layered film is microfabricated into acircular element with a diameter of 50 nm to 100 nm by aphotolithography process. In addition, an interlayer insulating film(SiN) is formed by a plasma CVD process while a resist remains. In theplasma CVD process, a reaction gas is a mixed gas of silane (SiH₄) andammonia (NH₃), the substrate is heated at 400° C., and a 13.56-MHzhigh-frequency power source and a 250-kHz low-frequency power source areused as a power source for generating plasma to generate plasma with atotal output of about 1 kW to 2.5 kW. After the interlayer insulatingfilm is formed with a thickness of about 100 nm, the resist used in theprevious photolithography process is cleaned with acetone or NMP. Then,Ta (10 nm), Cu (500 nm), and Ta (10 nm) films are formed in this orderby magnetron sputtering and a Ta/Cu/Ta multi-layered portion isprocessed in a bit line shape by photolithography. In this way, themagnetic memory element according to Example 3 is manufactured.

Next, the effect of the magnetic memory element according to Example 3will be described. When the magnetic layer (TbFeCo and FeCoB) is formedon the warped Si substrate 15 and the Si substrate 15 returns to a flatstate, a compressive stress σ generated in the magnetic layer can becalculated from the formula of mechanics of materials:

$\begin{matrix}{\sigma = {\frac{h_{S}^{2}}{6h_{f}R}\frac{E}{1 - \gamma}}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack\end{matrix}$

(where h_(S) is the thickness of a substrate, h_(f) is the thickness ofa thin film, γ is the Poisson's ratio, E is the Young's modulus, and Ris a curvature radius).

In the expression, when the thickness of the substrate is 300 μm, thethickness of the thin film is 5 nm, the Poisson's ratio γ is 0.3, theYoung's modulus E is 98 GPa (the typical value of iron), and thecurvature radius R is 2 m, a compressive stress of 210 GPa is generated.Similar to the above, when the compressive stress is converted intomagnetic anisotropy energy, the magnetic anisotropy energy is improvedby about 2.1×10⁵J/m³ (=2.1×10⁶ erg/cm³). As a result, thermal stabilityis improved.

Example 4

An MRAM according to Example 4 which is manufactured by the fourthembodiment of the invention has a structure shown in FIG. 8. An exampleof a method of manufacturing the structure shown in FIG. 8 will bedescribed below. A method of manufacturing a magnetic memory elementintegrated into an MRAM chip may be the same as that in Examples 1 to 3,or the magnetic memory element may be manufactured by the methodaccording to the related art. After a process of forming a bit lineends, the Si substrate is diced into chips. Then, an MRAM chip 1 isfixed to a die frame 41 made of, for example, copper phosphate by silverpaste. After the MRAM chip 1 is connected to a lead frame 43 by bondingwires 42, a resin flows into a mold with the die frame 41 being warpedin a concave shape with a curvature radius R of 2 m in the mold, therebysealing the chip. In this way, the magnetic memory element according toExample 4 is manufactured.

The effect of the MRAM according to Example 4 shown in FIG. 8 will bedescribed below. A compressive stress generated in the magnetic layer(TbFeCo or FeCoB) in the MRAM chip 1 which is warped together with thedie frame 41 can be calculated by Expression 1. As a result of thecalculation, it is expected that each magnetic memory element of theMRAM according to Example 4 will have the effect of improving thermalstability, similar to Example 3, that is, magnetic anisotropy energywill be improved by about 2.1×10⁵ J/m³ (=2.1×10⁶ erg/cm³).

The simplest method of checking the degree of strain of the magneticlayer is to measure a lattice constant using cross-section TEM. Thestrain is easily calculated by comparing a bulk lattice constant withthe lattice constant measured by cross-section TEM. However, it isdifficult to apply this method to an amorphous magnetic body.

Another method is to measure magnetization characteristics using, forexample, VSM (Vibrating Sample Magnetometer) or SQUID (SuperconductingQuantum Interference Device). FIG. 11 shows an example of themeasurement of magnetization characteristics, in which a solid lineindicates the magnetization characteristics in the easy magnetizationaxis direction and a dotted line indicates the magnetizationcharacteristics in the hard magnetization axis direction. In this case,an anisotropy field Hk may be measured as follows. A normal line at theorigin of the magnetization characteristics in the hard magnetizationaxis direction is extrapolated and the intensity of the magnetic fieldat an intersection point with the magnetization characteristics in theeasy magnetization axis direction is measured as the anisotropy fieldHk. When the anisotropy field Hk is calculated, magnetic anisotropyenergy Ku may be calculated by a relational expression Ku=2MsHk. In arare earth-transition metal alloy (TbFeCo, TbFe, GdFeCo, GdFe, DyFeCo,or DyFe), magnetic anisotropy energy is determined by a composition andan internal stress. Therefore, films with the same composition,thickness, and structure (for example, TbFeCo (5 nm), FeCoB (1 nm), MgO(1 nm), FeCoB (1 nm), TbFeCo (5 nm), Ta (5 nm), and Ru (5 nm)) areformed on the entire surface of a glass substrate, and a variation inmagnetic anisotropy energy is calculated from the magnetic anisotropyenergy of the entire film and the magnetic anisotropy energy of themagnetic memory element. When the same film structure is used, avariation in magnetic anisotropy energy is a variation in magnetoelasticenergy. Therefore, it is possible to indirectly measure a variation ininternal stress from the following relationship: magnetoelastic energyH_(el)=−(3/2)λσ, and it is possible to estimate a strain S from theYoung's modulus E and internal stress σ since the relationship S=Eσ isestablished between the internal stress σ and the strain S.

The embodiments of the invention have been described above, but theinvention is not limited to the above-described embodiment. Variousmodifications and changes of the invention can be made without departingfrom the scope and spirit of the invention.

The invention claimed is:
 1. A magnetic memory element comprising: alower electrode; an upper electrode; a magnetic tunnel junction portionbetween the lower electrode and the upper electrode, wherein themagnetic tunnel junction portion includes a first magnetic layer, aninsulating layer on the first magnetic layer, and a second magneticlayer on the insulating layer; and an interlayer insulating filmconfigured to apply compressive stress to opposite sides of the first orsecond magnetic layers in a one-axis direction of an in-plane directionof the first or second magnetic layers so as to contract the first orsecond magnetic layer along the one-axis direction and elongate thefirst or second magnetic layer in an easy-magnetization direction. 2.The magnetic memory element of claim 1, wherein at least one of thefirst or second magnetic layers is strained and deformed into anelliptical or rectangular in-plane shape defining a long axis associatedwith the easy-magnetization direction and a short axis such that therespective magnetic layer is elongated in a direction along the longaxis direction of the in-plane shape.
 3. The magnetic memory element ofclaim 1, wherein the first or second magnetic layer is a single-layerfilm made of a rare earth-transition metal alloy or a multi-layered filmof a rare earth-transition metal alloy and a spin-polarized film.
 4. Themagnetic memory element of claim 3, wherein the first or second magneticlayer is a multi-layered film of a rare earth-transition metal alloy anda FeCo alloy thin film or a FeCoB alloy thin film.
 5. The magneticmemory element of claim 1, wherein the first or second magnetic layer isa single-layer granular perpendicular magnetization film or amulti-layered film of a granular perpendicular magnetization film and aspin-polarized film, and wherein the easy-magnetization directioncorresponds to a perpendicular direction of the first or second magneticlayer.
 6. The magnetic memory element of claim 1, wherein: theeasy-magnetization direction is perpendicular to the first or secondmagnetic layers; and the first or second magnetic layer has a circularin-plane shape.
 7. The magnetic memory element of claim 1, wherein: theeasy-magnetization direction is perpendicular to the first or secondmagnetic layers; and the first or second magnetic layer has a squarein-plane shape.
 8. A storage device comprising: a plurality of magneticmemory elements, each magnetic memory element including: a lowerelectrode; an upper electrode; and a magnetic tunnel junction portionbetween the lower electrode and the upper electrode, wherein themagnetic tunnel junction portion includes a first magnetic layer, aninsulating layer on the first magnetic layer, and a second magneticlayer on the insulating layer; and a sealing package having theplurality of magnetic memory elements sealed therein, wherein thesealing package is configured to: draw at least one of the first andsecond magnetic layers; and contract at least one of the first andsecond magnetic layers in an in-plane direction.
 9. The storage deviceof claim 8, wherein at least one of the first or second magnetic layersis strained and deformed into an elliptical or rectangular in-planeshape defining a long axis and a short axis such that the respectivemagnetic layer is elongated in a direction along the long axis directionof the in-plane shape.
 10. The storage device of claim 8, furtherincluding a die frame on which a substrate having the plurality of themagnetic memory elements provided thereon is placed, wherein the sealingpackage has the die frame sealed therein.
 11. The storage device ofclaim 8, wherein the first magnetic layer or the second magnetic layeris a single-layer film made of a rare earth-transition metal alloy or amulti-layered film of a rare earth-transition metal alloy and aspin-polarized film.
 12. The storage device of claim 11, wherein thefirst magnetic layer or the second magnetic layer is a multi-layeredfilm of a rare earth-transition metal alloy and a FeCo alloy thin filmor a FeCoB alloy thin film.
 13. The storage device of claim 8, whereinthe first magnetic layer or the second magnetic layer is a single-layergranular perpendicular magnetization film or a multi-layered film of agranular perpendicular magnetization film and a spin-polarized film. 14.A storage device comprising: a plurality of magnetic memory elements;and a sealing package having the plurality of magnetic memory elementssealed therein, each magnetic memory element including: a lowerelectrode; an upper electrode; and a magnetic tunnel junction portionbetween the lower electrode and the upper electrode, wherein themagnetic tunnel junction portion includes a first magnetic layer, aninsulating layer on the first magnetic layer, and a second magneticlayer on the insulating layer; wherein the sealing material isconfigured to impart strain that elongates the first or second magneticlayer of at least one of the magnetic memory elements in a directionperpendicular to a surface of the respective magnetic layer such thatcompressive stress is generated and remains in an in-plane direction ofthe respective magnetic layer.
 15. The storage device of claim 14,wherein the first magnetic layer and the second magnetic layer areperpendicular magnetization films, and wherein at least one of the firstor second magnetic layers is strained and deformed so as to be elongatedin a direction perpendicular to a surface of the respectivemagnetization film.
 16. The storage of claim 14, wherein the firstmagnetic layer and the second magnetic layer are in-plane magnetizationfilms, and wherein at least one of the first or second magnetic layersis strained and deformed into an elliptical or rectangular in-planeshape defining a long axis and a short axis such that the respectivemagnetic layer is elongated in a direction along the long axis directionof the in-plane shape.
 17. The storage device of claim 14, wherein thefirst magnetic layer or the second magnetic layer is a single-layer filmmade of a rare earth-transition metal alloy or a multi-layered film of arare earth-transition metal alloy and a spin-polarized film.
 18. Thestorage device of claim 17, wherein the first magnetic layer or thesecond magnetic layer is a multi-layered film of a rare earth-transitionmetal alloy and a FeCo alloy thin film or a FeCoB alloy thin film. 19.The storage device of claim 14, wherein the first magnetic layer or thesecond magnetic layer is a single-layer granular perpendicularmagnetization film or a multi-layered film of a granular perpendicularmagnetization film and a spin-polarized film.
 20. The storage device ofclaim 19, wherein the first magnetic layer or the second magnetic layeris a multi-layered film of a granular perpendicular magnetization filmand a FeCo alloy thin film or a FeCoB alloy thin film.